Acceleration of Citrate Oxidation in Yeast by Aspartic Acid

Abstract

CITRATE oxidation in cell-free extracts of Saccharomyces cerevisiae has previously been reported to be stimulated by a weakly basic factor present in boiled yeast juice¹. It was afterwards observed that ammonia accelerates citrate oxidation when added to the assay system for oxidation factor, and significant amounts of free ammonia were found in the boiled juice prepared from the D.C.L. commercial bakers' yeast investigated². In a further study of different strains of yeast, high oxidation factor activity has now been observed in ammonia-free extracts of Anheuser–Busch commercial bakers' yeast when added to a particulate-free enzyme from the same organism. In these preparations all activity is due to free L-aspartic acid, present in a concentration of 4.6 [µM/gm. yeast. The end-product of citrate oxidation in the presence of aspartic acid is glutamic acid. The reaction requires the addition of di- or tri-pyridine nucleotide coenzymes. This is illustrated in Fig. 1.